ORIGINAL: banktoturn
ORIGINAL: missil3
Based on the wind tunnel tests I have done using golf balls, the reduction in drag occurs only at higher reynold's numbers. There is a lot current research going on to include such flow control techniques in the latest aircraft but the problem is there is not enough data on how they will perform in actual flight. dimples on a wing will surely reduce drag but it would have increased icing effect which could lead to a catastrophic crash.
For one, dimples don't cause a turbulent flow they induce a turbulent boundary layer that reduces boundary layer seperation for high reynold's number ( higher velocities) . The flow is still smooth . I have some velocity and turbulence intensity graphs to back this up if you want.
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The results of your tests are the opposite of what one would expect. The CD of a sphere tends to go down as the Reynold's number increases, because the boundary layer becomes turbulent earlier at higher Reynolds numbers. This would reduce the impact of dimples at higher Reynolds' numbers, since the dimples have no effect once the boundary layer is turbulent.
A turbulent boundary layer IS turbulent flow. When dimples are used to reduce drag, they do so by causing turbulent flow in the boundary layer, which in turn delays flow separation. The flow within a turbulent boundary layer is not 'smooth'.
banktoturn
Actually the results obtained are what are expected. The CDof a sphere is much higher for higher Reynold's numbers. the flow becomes turbulent due to flow seperation which increases CD. The flow around a dimpled sphere is still smooth inspite of the turbulent boundary layer.At high reynold's numbers the flow is around dimpled ball is smoother than for a similar sphere.